The present invention relates to a method of protecting components connected to a car radio, which each have a microprocessor and are connected to the car radio via a bus.
It is known that car radios are subject to increased risk of theft. Therefore numerous safety (security) mechanisms are known to protect the car radio against theft; some of these have been in use. These include, for example, designing a car radio to have a removable operating part, a turn-on inhibiting circuit preventing the car radio from turning-on until an individual numeric code is entered, the capability of switching on the car radio only by using a key card, etc. It can therefore be assumed that the car radio itself is adequately protected against theft.
The constant improvement in music reproduction quality in car equipment has resulted for many years in the use of more and more expensive components with the car radio, whose values are comparable to or even higher then that of the car radio. Such components include active boxes, CD changers, navigation devices, external displays, etc.
The task at hand is to protect these components used with the car radio against theft, in the same way as the car radio itself is protected against theft. This would, however, be very inconvenient in that individual numerical codes would have to be entered in each component or each component would have to be switched on using a separate key card. Such a method is not practicable, so that no theft protection has so far been used for the components.
An object of the present invention is to provide theft protection for components connected to a car radio that is convenient to handle.
In a method according to the present invention, when the component is connected to a car radio for the first time, a specific identification signal is transmitted from the car radio to the component via the bus, this signal is stored in the component so it cannot be accessed by the user and, when the component is turned on again, the ID signal stored in the component is compared with that of the car radio and the component and/or the car radio can be turned on to be ready for operation only if the ID signal of the car radio is identical to that of the stored ID signal.
The present invention provides a theft protection method that uses the car radio, which is itself safe from theft, as a xe2x80x9cguardian.xe2x80x9d When it is connected to the car radio, a component new from the factory is assigned by the method according to the present invention to the car radio by the ID signal transmitted by the car radio and stored in the component. The component can only be operated as long as it remains connected to the car radio. Therefore, removing a component is useless, since it cannot be connected to another car radio so that it can still operate. Thus, the principle according to the present invention implements an anti-theft method that requires no additional action on the part of the user.
Should a component be legitimately connected to another car radio because the component has been sold or the owner of the component wishes to connect the latter to another car radio, for example, the initial assignment of the component to the car radio may be removed via the car radio recognized as belonging to the component. If such a release of the component using the car radio is no longer possible, since the latter is no longer operable, authorized dealers may release the component using a special decoder box upon presentation of evidence of ownership.
The comparison according to the present invention between the ID signal of the car radio and the ID signal stored in the component, which takes place when the car radio is turned on again may occur by the specific ID signal from the car radio to the component being repeated for the comparison to be made in the component. This procedure ensures greater security against manipulation compared to a comparison taking place in the car radio, which is also conceivable.
To reinforce the assignment between the component and the car radio, a specific ID signal can also be transmitted by the component to the car radio when the component is connected for the first time; this ID signal is stored in the car radio and compared to the ID signal transmitted again by the component to the car radio whenever the car radio is turned on again. Double comparison is thus achieved.
It may be convenient to transmit the ID signal sent from the car radio to be stored in the component with a one-way encryption, in order to prevent the ID signal of the respective car radio to be obtained through analysis of the stored data word in the component.